The present invention relates to sidewall insulation in the region between the outermost firing shaft and the outer wall of a chamber type furnace for baking carbon blocks, in particular anodes for the production of aluminum by the fused salt electrolytic process.
Chamber type furnaces for baking carbon blocks, used in particular as anodes in the electrolytic production of aluminum, have been known for many years. These comprize a plurality of chambers which are arranged in rows and are either built into the ground or directly on the ground. Between the baking chambers which hold the carbon blocks are firing shafts. The chambers are mostly vertical and, depending on their mode of construction, are either open at the top or are closed off there by removable lids.
In the production of the carbon blocks a doughy mixture is shaped into the form of blocks either in a press or in a vibration machine. The green strength carbon blocks are then transferred to the baking furnace where they are stacked in the baking chambers or pits and packed into a bed of coke or anthracite powder. Following this the baking chambers are then sealed off so as to be almost air tight. The packing in the carbonaceous powder prevents oxidation of the carbon blocks during the baking process. The heating is performed using gas, oil or electrical energy.
The baking process lasts several days, during which the temperature of the carbon blocks is for a specific time above 1100.degree. C. It is therefore necessary to take special measures to limit energy losses and to prevent the region immediately next to and around the furnace from being exposed to strong heating. For this reason it is normal to construct the furnace with relatively thick walls and floor using refractory, thermally insulating ceramic material.
Known from the Austrian Pat. No. 261 723 is a chamber type furnace with thick sidewall insulation of firebrick which has a high thermal capacity. On heating the furnace to operating temperature this thick firebrick insulation produces a pressure on the firing shaft as a result of which the latter can even be displaced from its vertical position.
FIG. 1 shows a partical vertical section through a chamber type furnace of another known form. A shell comprizing a base 10 and an outer wall 12 of concrete is fitted with a multilayered construction of firebricks 14 and sidewall insulation for example of foamed bricks 16 or other insulating bricks (in the following for simplicity referred to simply as foamed bricks). After a thick sidewall layer of firebricks 14 is the outermost firing shaft 18 which features a thinner wall of firebricks 14 on the side towards the interior of the furnace. After the first anode pit 20 in which the green strength carbon blocks are stacked, comes a normal firing shaft 22 which is walled on both sides with a thin wall of firebricks 14. The uppermost region of the furnace is protected by cover plates 24.
In the version of chamber furnace shown in FIG. 1 there are two types of firing shafts viz.; the lighter normal shaft 22 and the heavier outermost shaft 18 which is neighbored to the outer wall 12.
The object of the present invention is to develop a sidewall insulation for the region between the outermost firing shaft and the outer wall of a chamber type furnace for baking carbon blocks, in particular anodes for the fused salt electrolytic production of aluminum, such that the said insulation exhibits a higher degree of efficiency and longer service life, and this using conventional designs, and incurring comparable expenditure for labor and material.